Room-temperature-curable organopolysiloxane composition

ABSTRACT

A room-temperature-curable organopolysiloxane composition comprising:
         (A) an organopolysiloxane having 1.5 or more end groups having at least one hydroxyl group on the average;   (B) a silane or a siloxane oligomer having three or more silicon-bonded hydrolyzable groups;   (D) an inorganic powder; and either   (C) microparticles of thermoplastic resin containing a platinum compound having an average diameter from 0.1 to 20 μm; or   (C1) a platinum compound; and   (C2) an organosiloxane oligomer which contains aryl and alkenyl groups and has 8 or less silicon atoms in each molecule and which contains in each molecule at least one divalent organosiloxane as represented by the formula:
 
—(R 2 )(R 3 )SiO—(R 2 )(R 3 )Si—,
 
(where R 2  is an aryl group, and R 3  is an alkenyl group), in a quantity of at least 2 moles of component (C2) per 1 mole platinum atoms in component (C1).

The present invention relates to a room-temperature-curableorganopolysiloxane composition, in particular, to aroom-temperature-curable organopolysiloxane composition that is turned,after curing, into a cured silicone body with excellent flame-retardingproperties, which properties are not lost even after long-time exposureto high temperatures.

BACKGROUND ART

Room-temperature-curable organopolysiloxane compositions withflame-retarding properties imparted to them by adding a platinumcompound and an inorganic filler are known in the art. For example,Japanese Patent Application Publication No. (hereinafter referred to as“Kokai”) H4-18451 discloses a room-temperature-curableorganopolysiloxane composition consisting of a dimethylpolysiloxanehaving both molecular terminals capped with trimethoxysilyl groups,silica powder, quartz powder, zinc carbonate, a platinum compound (aplatinum-ethylene complex obtained by reacting chloroplatinic acid withethylene and dehydrochlorinating the reaction product), a triethylaminesalt, and dibutyltin dioctoate.

Furthermore, Kokai H5-230376 discloses a composition comprising adimethylpolysiloxane having both molecular terminals capped withhydroxyl groups, an alumina hydrate, carbon black, a platinum compound{a complex of platinum with a vinylsiloxane(1,3-divinyl-1,1,3,3-tetramethyidisiloxane)}, andmethyltris-(methylethylketoxime)-silane.

Another publication, Kokai H5-125285 discloses aroom-temperature-curable organopolysiloxane composition consisting of adimethylpolysiloxane having both-molecular terminals capped withhydroxyl groups, aluminum hydroxide powder, calcium carbonate, aplatinum compound (an isopropanol solution of chloroplatinic acid), andvinyltris-(methylethylketoxime) silane.

However, the aforementioned room-temperature-curable organopolysiloxanesadmixed with platinum compounds normally have low storage stability, andafter long-term storage, are subject to gradual decrease inflame-retarding properties. In particular, flame-retarding propertiesdrop most significantly in a cured body made from the aforementionedcomposition after long-term storage at high temperatures. This limitsthe field of application of the aforementioned compositions.

It is an object of the present invention to provide aroom-temperature-curable organopolysiloxane characterized by excellentflame-retarding properties which are preserved in a cured siliconearticle, made from the aforementioned composition, even after long-termstorage at high temperatures.

DISCLOSURE OF THE INVENTION

The above problems can be solved by admixing a room-temperature-curableorganopolysiloxane composition with a flame-retarding agent in the formof specific finely-divided particles of thermoplastic resin containing aplatinum compound.

The present invention relates to a room-temperature-curableorganopolysiloxane composition comprising:

-   -   (A) 100 parts by weight of an organopolysiloxane having a        viscosity from 100 to 500,000 mPa·s at 25° C. and having in one        molecule 1.5 or more end groups represented by the general        formula: (X)_(a)R¹ _(3−a)Si—, where        -   each X is independently a hydroxyl group or a hydrolyzable            group,        -   each R¹is independently a monovalent hydrocarbon group or a            halogen-substituted monovalent hydrocarbon group, and        -   a is 1, 2, or 3;    -   (B) 0.01 to 40 parts by weight of a cross-linking agent selected        from a silane or a siloxane oligomer, where        -   the cross-linking agent has three or more silicon-bonded            hydrolyzable groups per molecule; and    -   (C) microparticles of a thermoplastic resin containing a        platinum compound in such an amount that the content of metallic        platinum in component (C) is within the range of 0.01 to 5 wt.        %, where        -   the microparticles have an average diameter from 0.1 to 20            μm,        -   component (C) is present in an amount sufficient to provide            1 to 2,000 ppm of metallic platinum in the composition; and    -   (D) 5 to 300 parts by weight of an inorganic powder.

The present invention further relates to a room-temperature-curableorganopolysiloxane composition comprising:

-   -   (A) 100 parts by weight of an organopolysiloxane having a        viscosity from 100 to 500,000 mPa·s at 25° C. and having in one        molecule 1.5 or more end groups represented by the following        general formula: (X)_(a)R¹ _(3−a)Si—, where        -   each X is independently hydroxyl group or a hydrolysable            group,        -   each R¹ is independently a monovalent hydrocarbon group or a            halogen-substituted monovalent hydrocarbon group, and        -   a is 1, 2, or 3;    -   (B) 0.01 to 40 parts by weight of a cross-linking agent selected        from silane or a siloxane oligomer, where        -   the cross-linking agent has three or more silicon-bonded            hydrolyzable groups per molecule;            -   (C1) a platinum compound present in an amount such that                metallic platinum is present in an amount of 1 to 2,000                ppm based on the weight of the composition;            -   (C2) an organosiloxane oligomer, where                -   the organosiloxane oligomer contains aryl and                    alkenyl groups,                -   the organosiloxane oligomer has 8 or less silicon                    atoms per molecule, and                -   the organosiloxane oligomer contains in each                    molecule at least one divalent organosiloxane group                    represented by the formula                    —(R²)(R³)SiO—(R²)(R³)Si—,                -   where R² is an aryl group, and                -   R³ is an alkenyl group;            -   where the organosiloxane oligomer is present in a                quantity such that the composition contains at least 2                moles of component (C2) per 1 mole of platinum atoms in                component (C1); and    -   (D) 5 to 300 parts by weight of an inorganic powder.

In accordance with the invention, component (A) is an organopolysiloxanehaving a viscosity from 100 to 500,000 milliPascal·seconds (mPa·s) at25° C. and having in one molecule 1.5 or more end groups represented bythe following general formula: (X)_(a)R¹ _(3−a)Si—, wherein X is ahydroxyl group or a hydrolyzable group, R¹ is a monovalent hydrocarbongroup or a halogen-substituted monovalent hydrocarbon group, and a is 1,2, or 3. Cross-linking occurs when component (A) reacts with component(B). In the above formula, R¹ can be represented by a monovalenthydrocarbon group such as methyl group, ethyl group, isopropyl group,hexyl group, octadecyl group, or a similar alkyl group; vinyl group,hexenyl group, or a similar alkenyl group; cyclohexyl group, cyclopentylgroup, or a similar cycloalkyl group; benzyl group, β-phenylethyl group,or a similar arylalkyl group; phenyl group, tolyl group, or a similararyl group. In the above formula, R¹may also comprise ahalogen-substituted monovalent hydrocarbon (with a hydrogen atom of thisgroup being substituted by a halogen atom) such as 1,1,1-trifluoropropylgroup, perfluoropropyl group, or a similar organic group. In onemolecule, the aforementioned R¹ groups can be the same or different. Inthe above formula, X designates hydroxyl group, or an alkoxy group,oxime group, acetoxy group, propenyloxy group, amino group, aminoxygroup, amido group, or a similar hydrolyzable group. For ease ofsynthesis and for better balance of mechanical properties, it isrecommended that a majority of all R¹ groups be methyl groups.

A typical example of the aforementioned organopolysiloxane is adiorganopolysiloxane represented by the following general formula:(X)_(a)R¹ _(3−a)SiR″—(R₂SiO)_(n)—R₂SiR″SiR¹ _(3−a)(X)_(a),

where R¹ and X are the same as defined above, and R″ is oxygen atom oran alkylene group. R is the same monovalent hydrocarbon group or ahalogen-substituted monovalent hydrocarbon group as R¹; a is 1, 2, or 3;and n is such a value that provides 25° C. viscosity of theaforementioned organopolysiloxane within the range of 100 to 500,000mPa·s, preferably within the range of 500 to 100,000 mPa·s. The presentcomponent may comprise a mixture of compounds with different degrees ofpolymerization and with different viscosities, or a mixture of compoundshaving different substituents.

Methods of preparation of such diorganopolysiloxanes are known in theart. For example, a diorganopolysiloxane where X is hydroxyl group andR″ is oxygen atom in the above formula, can be easily produced by anequilibrium polymerization of octamethylcyclotetrasiloxane with the useof an alkali or an acidic catalyst in the presence of water or a silanecompound as a polymerization stopping agent. Similarly, adiorganopolysiloxane where X is an alkoxy group and R″ is oxygen atom inthe above formula, can be produced by means of dealcoholization andcondensation of a silanol-capped diorganopolysiloxane with atetraalkoxysilane, alkyltrialkoxysilane, or a dialkyldialkoxysilane inthe presence of a condensation-reaction catalyst. Furthermore, adiorganopolysiloxane where X is an alkoxy group and R″ is ethylene groupin the above formula can be produced by means of a hydrosilylationreaction of a vinyl-capped diorganopolysiloxane with ahydrogentrialkoxysilane, a hydrogenmethyldialkoxysilane, or ahydrogendimethylalkoxysilane in the presence of a platinum-compoundcatalyst.

Component (B) is a silane or a siloxane oligomer that functions as across-linking agent. The following are specific examples of such silanesor siloxane oligomers: tetramethoxysilane, tetraethoxysilane,methyltrimethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane,3,3,3-trifluoropropyltrimethoxysilane, β-cyanoethyltrimethoxysilane,tetraisopropoxysilane, tetrabutoxysilane, phenyltrimethoxysilane,octadecyltrimethoxysilane, tetra (β-chloroethoxy) silane, tetra(2,2,2-trifluoroethoxy) silane, propyltris (δ-chlorobutoxy) silane,methyltris (methoxyethoxy) silane, or a similar alkoxysilane;methylpolysilicate, dimethyltetramethoxydisiloxane, or a similaralkoxysiloxane; methyltris (methylethylketoxime) silane, vinyltris(methylethylketoxime) silane, phenyltris (methylethylketoxime) silane,methyl (diethylketoxime) silane, tetra (methylethylketoxime) silane,methyltris (cyclohexylamino) silane, vinyltris (n-butylamino) silane,methyltris (N-butylacetoamide) silane, methyltris(N-cyclohexylacetoamide) silane, methyltris (N,N-diethylaminoxy) silane,1,2,3,4-tetramethyl-1-ethyl-2,3,4-tris (N,N-diethylaminoxy)cyclotetrasiloxane, methyltri (isopropenoxy) silane, vinyltris(isopropenoxy) silane; and products of partial hydrolyzation andcondensation of the aforementioned compounds. It is recommended to addthis component in an amount from 0.01 to 40 parts by weight, preferably0.1 to 15 parts by weight for each 100 parts by weight of component (A).

Component (C) is in the form of microparticies of a thermoplastic resincontaining a platinum compound. This component imparts flame-retardingproperties to a cured body formed from the composition of the presentinvention. Particles of component (C) comprise a platinum compound and athermoplastic resin and have an average diameter from 0.1 to 20micrometers (μm). They contain a platinum compound in such an amountthat the content of metallic platinum therein is within the range of0.01 to 5 wt. %. The aforementioned range of the particle diameter isrecommended because, if the particle diameter is less than 0.1 μm, itwould be difficult to admix this component in an uncured state, and ifthe particle diameter exceeds 20 μm, then it would be difficult toefficiently expel the platinum compound from the microparticles of thethermoplastic resin during burning, whereby flaine-retarding propertieswill be reduced. As has been mentioned above, it is recommended to use aplatinum compound in such an amount that the content of metallicplatinum therein is within the range of 0.01 to 5 wt. %, in particular,from 0.05 to 2 wt. %. If the metallic platinum is contained in an amountless than 0.01 wt. %, the addition of the aforementionedplatinum-containing microparticles of the thermoplastic resin will notnoticeably improve the flame-retarding properties, and if the addedamount exceeds 5 wt. %, it would be difficult to retain the platinumcompound within the microparticles of the thermoplastic resin.

Although there are no special limitations with regard to the shape ofthe platinum-containing microparticles of the thermoplastic resinas-component (C), it is recommended, from the point of view of betterreproducibility of stable flame-retarding properties, to use particlesof a spherical shape.

Component (C) should be used in such an amount that the content of theplatinum compound in component (C) would correspond to 1 to 2,000 ppm ofmetallic platinum in the composition. The content of the metallicplatinum in an amount of less than I ppm will not provide sufficientflame-retardation properties, while the content of metallic platinumexceeding 2000 ppm will decrease flame-retarding properties and will notbe economically justified.

There are no special restrictions with regard to the type of thethermoplastic resin that constitutes component (C), provided that thisresin acquires plasticity when heated. However, thermoplastic resinsthat poison or deactivate the platinum compounds are not recommended foruse. The aforementioned thermoplastic resins preferably have a glasstransition point within the range from 40 to 250° C. If the glasstransition point is below 40° C., it would be difficult to produce themicroparticles of the thermoplastic resin, and they may melt under theeffect of shear heat generated during mixing with other components. Ifthe glass transition point exceeds 250° C., it would be difficult toefficiently release the platinum compound and obtain improvedflame-retarding properties.

Thermoplastic resins suitable for use in component (C) can berepresented by a silicone resin, polysilane resin, polycarbonate resin,poly(methylmethacrylate) resin, a copolymer of methylmethiacrylate andbutylmethacrylate, or a similar acrylic-type resin, a polyester resin,polyethylene resin, polystyrene resin, poly(vinylchloride),poly(vinylidene chloride), a copolymer of vinylchloride and vinylidenechloride, a poly(acrylonitrile) resin, a copolymer of an allylonitrileand a styrene, a copolymer of acrylonitrile and styrene; a copolymer ofacrylonitrile, butadiene, and styrene; a polyamide resin, celluloseacetate, or a similar cellulose ester resin, a celluloseacetate butyrateresin, and a poly(phenyleneoxide) resin.

The silicone resin suitable for use in component (C) can be exemplifiedby a resin composed of monophenylsiloxane units, diphenylsiloxane units,and dimethylsiloxane units, a resin composed of monophenylsiloxane unitsand dimethylsiloxane units, and a resin composed of monophenylsiloxaneunits and methylvinylsiloxane. The polysilane resin can be represented,e.g., by a resin composed of methylphenylsilane units and dimethylsilaneunits. Most preferable among the above are silicone and polycarbonateresins, while of these two, polycarbonate resins are characterized bythe highest flame-retarding and heat-resistant properties.

The platinum compound of component (C) can be represented bychloroplatinic acid, an alcohol-modified chloroplatinic acid, an olefincomplex of platinum, a diketone complex of platinum or chloroplatinicacid, and a divinyltetraorganodisiloxane (e.g.,1,3-divinyltetramethyidisiloxane) complex of platinum or chloroplatinicacid. The divinyltetraorganodisiloxane complex of platinum orchloroplatinic acid, which is the most preferable from the point of viewof higher activity and better flame-retarding properties, can beprepared by a method described in Kokai H11-42436, i.e., by causing areaction between the chloroplatinic acid and thedivinyltetraorganodisiloxane in an alcoholic solution and in thepresence of sodium bicarbonate. The reaction product is then combinedwith toluene, and the alcohol is removed by distillation. As a result, adivinyltetraorganodisiloxane complex of platinum is produced.

Platinum-containing microparticles of the thermoplastic resin ascomponent (C) and methods of its preparation are known in the art. Forexample, as described in Kokai S58-37053, such particles can be producedby dissolving a platinum compound and a thermoplastic silicone resin intoluene, drying the obtained solution, thus obtaining a solid substancecomprising the platinum compound and the thermoplastic silicone resin,and then grinding the obtained solid substance.

Another method, described in Kokai H2-4833, consists of dissolving aplatinum compound and a thermoplastic silicone resin in alow-boiling-point solvent such as methylene chloride, dripping theobtained solution into an aqueous solution of a surface-active agent,thus producing an oil/water emulsion, gradually removing the solvent,and recovering the platinum and the resin in the form of microparticles.

A method disclosed in Kokai H4-29748 and Kokai H7-41678 consists ofdissolving a platinum compound and a thermoplastic resin in toluene,dichloromethane, or a similar solvent, spraying the solution into a hotflow of nitrogen gas in a spray dryer, and producing the microparticlesby evaporating the solvent.

Component (C) should be used in such an amount that the content of theplatinum compound in component (C) would correspond to 1 to 2,000 ppm ofmetallic platinum in the composition. This is because the content of themetallic platinum in an amount of less than 1 ppm will not providesufficient flame-retardation properties, while the content of metallicplatinum exceeding 2000 ppm will decrease flame-retarding properties andwill not be economically justified.

Component (C1) and Component (C2) may also be used for impartingflame-retarding properties to a cured body formed from the compositionof the present invention, instead of Component (C).

Component (C1) imparts flame-retarding properties to an article obtainedby curing the composition of the invention. Component (C1) can beexemplified by a chloroplatinic acid, alcohol-modified chloroplatinicacid, a platinum complex of olefin, a platinum or a chloroplatinic-acidcomplex of diketone, and platinum or chloroplatinic acid complex of1,3-divinyltetramethyidisiloxane. Most preferable among the abovecompounds is a platinum complex having as a ligand an organosiloxanewhich contains alkyl and alkenyl groups having in one molecule at leastone divalent organosiloxane group as shown by the following formula:—(R³)(R⁴)SiO—(R³)(R⁴)Si—,where R⁴ is an alkyl group with 6 or less carbon atoms, and R³ is thesame as defined above, and containing in one molecule an alkyl group andan alkenyl group with 8 or less silicon atoms, or a mixture of theaforementioned organosiloxane with the aforementioned platinum complex.This component (C1) may be the aforementioned platinum complex, but itmay also be a mixture of the aforementioned platinum complex withorganosiloxane oligomer identical to or of the same type as the(alkyl+alkenyl)-containing organosiloxane oligomer coordinated in theplatinum complex. (Alkyl+alkenyl)-containing organosiloxane oligomer notcoordinated within the platinum complex should be present generally atno more than 30 moles per 1 mole platinum atoms in the platinum complex.

It is known in the art to produce component (C1) by reacting, withheating, an (alkyl+alkenyl)-containing organosiloxane oligomer with ahaloplatinic acid or a haloplatinic acid salt (see Japanese PatentPublication No. (hereinafter referred to as “Kokoku”) S42-22924). In thepreparation of component (C1) by this method, the alkenyl group in thestarting (alkyl+alkenyl)-containing organosiloxane oligomer is generallyvinyl group. Moreover, it is preferred that the alkyl group be methylgroup considering the economics and prevention of side reactions duringpreparation of component (C1). Although no specific restriction isplaced on groups which may be present in addition to the alkenyl andalkyl groups, it is necessary in particular to avoid aryl groups sincethis causes a reduction in the platinum yield in the preparation ofcomponent (C1).

Examples of this (alkyl+alkenyl)-containing organosiloxane oligomer are1,3-divinyltetramethyldisiloxane and1,3,5,7-tetravinyltetramethylcyclotetrasiloxane. It is recommended toadd component (C1) in such an amount that the content of metallicplatinum is within the range of 1 to 2000 ppm based on the weight of thecomposition. The content of the metallic platinum in an amount of lessthan 1 ppm will not provide sufficient flame-retardation properties,while the content of metallic platinum exceeding 2000 ppm will decreaseflame-retarding properties and will not be economically justified.

Component (C2) is added for improving stability of component (C1).Component (C2) is an organosiloxane oligomer which contains aryl andalkenyl groups and has 8 or less silicon atoms in each molecule andwhich contains in each molecule at least one divalent organosiloxanegroup as represented by the formula:—(R²)(R³)SiO—(R²)(R³)Si—,where R² is an aryl group, and R³ is an alkenyl group. Component (C2) isadded in a quantity of at least 2 moles of component (C2) per 1 moleplatinum atoms in component (C1). In the above formula, the aryl groupcan be represented by phenyl group and tolyl group. The phenyl group ispreferable. The alkenyl group can be represented by vinyl group, allylgroup, butenyl group, and hexenyl group. Of these, the vinyl group ispreferable. The aforementioned organopolysiloxane can be exemplified by1,3-divinyl-1,3-diphenyldimethyldisiloxane and1,3-divinyltetraphenyidisiloxane.

Components (C1) and (C2) can be mixed directly with components (B) and(D). Alternatively, components (C1) and (C2) may be premixed, asdisclosed in Japanese Patent No. 2974692. The obtained mixture can befurther mixed with components (A), (B), and (D). Furthermore, whencomponent (C1) is a platinum complex having as a ligand anorganosiloxane oligomer which contains alkyl and alkenyl groups havingin one molecule at least one divalent organosiloxane group shown by thefollowing formula:—(R³)(R⁴)SiO—(R³)(R⁴)Si—,(where R⁴ is an alkyl group with 6 or less carbon atoms, and R³ is thesame as defined above) and containing in one molecule an alkyl group andan alkenyl group with 8 or less silicon atoms, components (C1) and (C2)can be mixed, and after the organosiloxane oligomer contained incomponent (C1) is removed from the obtained mixture by distillation invacuum, the mixture can be further mixed with components (A), (B), and(D). Thus, according to the latter method, a platinum catalystcomposition with an even more superior storage stability can be preparedby removal of part of the platinum-coordinated(alkyl+alkenyl)-containing organosiloxane oligomer and part or all ofthe non-platinum-coordinated (alkyl+alkenyl)-containing organosiloxaneoligomer in component (C1) and by substitution with the(phenyl+alkenyl)-containing organosiloxane oligomer of component (C2).The platinum catalyst composition of the aforementioned type ischaracterized by a better high-temperature stability and a betterstability against other substances present in the system than theplatinum/siloxane complexes known from the art.

The inorganic powder, component (D), improves flowability of thecomposition of the invention prior to curing and improves mechanicalproperties and flame-retarding properties after curing. The followingare examples of appropriate inorganic powders: dry-process silicapowder, wet-process silica powder, or a similar reinforcing silicapowder; quartz powder; diatomaceous earth; aluminum oxide, iron oxide,zinc oxide, titanium oxide, cerium oxide, or a similar metal oxidepowder; magnesium hydroxide, aluminum hydroxide, or a similar metalhydroxide powder; calcium carbonate, zinc carbonate, or a similarcarbonate powder; talc, clay, mica, carbon black, glass beads; quartz,silica, or similar powders surface-treated with a hydrophobic agent suchas trimethylchlorosilane, dimethyidichlorosilane,dimethyldimethoxysilane, hexamethyldisilazane, oroctamethylcyclotetrasiloxane, as well as a calcium carbonate powdersurface-treated with a fatty acid, or a resin acid. Most preferablyamong the above are dry-process silica powder, wet-process silicapowder, or a similar reinforcing silica powder, quartz powder, ceriumoxide powder, titanium oxide powder, carbon black, aluminum oxidepowder, aluminum hydroxide powder, magnesium hydroxide powder, calciumcarbonate powder, magnesium carbonate powder, and zinc carbonate powder.The dry-process silica powder, especially the one having the surfacetreated with the aforementioned hydrophobic agent is preferable. And theaforementioned dry-process silica powder can be used in combination withother powders mentioned above (such as quartz powder, cerium oxidepowder, titanium oxide powder, carbon black, or a mixture thereof). Themost preferable for component (D) is a mixture of dry-process silicapowder, quartz powder, cerium oxide powder, and carbon black, and amixture of dry-process silica powder, quartz powder, cerium oxidepowder, carbon black, and titanium oxide powder.

If the amount of aforementioned component (D) added to the compositionis too small, it would be impossible to improve mechanical strength andflame-retarding properties, and if it is used in an excessive amount,the composition will be too viscous and will be difficult to handle inproduction. Therefore, it is recommended to add component (D) in anamount of 5 to 300 parts by weight for each 100 parts by weight ofcomponent (A). When component (D) consists of particles having amicroscopic diameter, such as a reinforcing silica, light calciumcarbonate, or carbon black, it should be used in an amount of 5 to 60parts by weight. If the particles have a relatively large diameter, itshould be used in an amount of 10 to 200 parts by weight.

To increase elongation and to lower the modulus of elasticity, thecomposition of the present invention can be additionally combined withbifunctional silanes, siloxanes, or both. Such bifunctional silanes andsiloxanes can be represented by the following compounds: dimethylbis(N-methylacetoamide silane), dimethylbis (N-ethylacetoamide) silane,diphenylbis (diethylaminoxy) silane, methylphenylbis (diethylaminoxy)silane, 1,2,3,4-tetramethyl-1,2-diethyl-3,4-bis (N,N-diethylaminoxy)cyclotetrasiloxane, diphenyldimethoxysilane, dimethyidimethoxysilane,and a diorganopolysiloxane capped only at one molecular terminal withsilicon-bonded hydroxyl group or a hydrolyzable group. It is recommendedthat such additional components be used in an amount of 0.01 to 20 partsby weight for each 100 parts by weight of component (A). The mostoptimum amount of the aforementioned additional components is selectedwith reference to concentration of hydroxyl groups and hydrolyzablegroups in component (A) and to the content of moisture in thecomposition.

If necessary for acceleration of the condensation reaction betweencomponents (A) and (B), the composition of the present invention can beadditionally combined with a condensation-reaction-accelerating catalyst(curing promotion catalyst). The following are examples of theaforementioned catalysts: lead-2-ethyloctoate, dibutyltin dilaurate,dibutyltin-2-ethylhexoate, dibutyltin dilaurate,dibutyltindiacetylacetoate, dibutyltin tri-2-ethylhexoate,iron-2-ethylhexoate, cobalt-2-ethylhexoate, manganese-2-ethylhexoate,stannous caprylate, tin naphthenate, tin oleate, zinc naphthenate, zincstearate, titanium naphthenate, or a similar metal salt of amonocarboxylic acid; tetrabutyl titanate, tetraphenyl titanate,tetra-2-ethylhexyl titanate, tetraoctadecyl titanate, triethanolaminetitanate, ethyleneglycol titanate, diisopropoxybis (ethylacetate)titanium, diisopropoxybis (acetylacetone) titanium, dibutoxybis(methylacetoacetate) titanium, or a similar organic titanium compound;hexylamine, dodecylamine, or a similar amine, hexylamine acetate,dodecylamine phosphate, or a similar amine salt; benzyltrimethylammoniumacetate, or a similar quaternary ammonium salt; and potassium acetate,or a similar alkali metal salt. The aforementioned catalysts may bemixed in an amount of from 0.001 to 10 parts by weight, and preferablyfrom 0.01 to 10 parts by weight, preferably 0.01 to 5 parts by weight,for each 100 parts by weight of the component (A).

If necessary, within the limits not detrimental to the objects of theinvention, the composition of the present invention may incorporateother conventional additives, which are normally added toroom-temperature-curable organopolysiloxane compositions, such aspigments, flame-retarding agents, heat-resistance improvers,thermal-conductivity improvers, adhesive promoters, thixotropyimparters, curing retarders, etc. The room-temperature-curablecomposition of the present invention may constitute a single-liquid ortwo-liquid type composition. Furthermore, the composition may be of asag type or a non-sag type.

After curing, the room-temperature-curable organopolysiloxanecomposition of the invention described above demonstrates excellentflame-retarding properties, which are not lost in a cured product evenafter long-time exposure to high temperatures. Therefore, thecomposition of the invention may find application in the areas wheresuch properties are desirable, e.g., for the production of coatings,seals, and adhesives used in electric and electronic devices.

BEST MODE OF CARRYING OUT THE INVENTION

The invention will be further described in more detail with reference topractical and reference examples. In these examples, all parts will beparts by weight, and all viscosities correspond to values measured at25° C.

Flame-retarding properties of the room-temperature-curableorganopolysiloxane compositions were measures by the method specified byUL-94.

Initial Flame-Retarding Properties

The room-temperature-curable organopolysiloxane composition was loadedinto a sheet-formation mold and cured for 7 days at 60% relativehumidity and at 25° C. As a result, a 0.8 millimeter-thicksilicone-rubber sheet was produced. This sheet was cut to form 127millimeter-long, 12.7 millimeter-wide, and 0.8 millimeter-thickspecimens.

Each specimen was fixed vertically in a clamp and ignited from below for10 seconds (sec.) by the flame of a burner operating on a gaseousmethane. The flame height was 20 millimeters (mm). The burner wasremoved, and the time in seconds until the flame on the specimen wasextinguished was measured. Directly after extinguishing, the ignitiontest was repeated for 10 sec., and the time until the flame on thespecimen was extinguished was measured again. Such test was performed on5 specimens with 10 time-measurement tests. The maximum value out of 10measurements was taken as the maximum flame-retarding time.

Flame-Retarding Properties after Curing

The 127 mm-long, 12.7 mm-wide, and 0.8 mm-thick specimens obtained formeasurement of the initial flame-retarding properties were placed into a70° C. heating oven and heated for 7 days. The specimens were removedand their heat-retarding properties were measured in the same manner asdescribed above. Furthermore, the 127 mm-long, 12.7 mm-wide, and 0.8mm-thick specimens obtained for measurement of the initialflame-retarding properties were placed into a 150° C. heating oven andheated for 21 days. The specimens were removed and their heat-retardingproperties were measured in the same manner as described above.

REFERENCE EXAMPLE 1

Preparation of Microparticles of a Platinum-Containing ThermoplasticSilicone Resin

A 60 weight % (wt. %) toluene solution of a thermoplastic silicone resinwas prepared by dissolving in toluene a thermoplastic silicone resinrepresented by the following average composition formula:(PhSiO_(3/2))_(0.78)(Me₂SiO)_(0.22) (where Ph is phenyl group, and Me ismethyl group) and having the glass transition point of 65° C.

A uniform solution of a thermoplastic silicone resin and a platinumcompound was produced by adding 0.25 kilograms (kg) of1,3-divinyltetramethyidisiloxane, 250 kg of dichloromethane, and 10.0 kgof toluene solution of platinum-1,3-divinyltetramethyldisiloxane complex(with a 2.0 wt. % platinum metal and a 6.0 wt. %1,3-divinyltetramethyldichlorosilane) to 83.3 kg of the aforementionedtoluene solution of the thermoplastic silicone resin.

The obtained uniform solution was continuously sprayed via a dual-flownozzle into a spray-dryer through which heated nitrogen gas wasdirected. The temperature of the nitrogen gas was 80° C. at the spraydryer's inlet and 50° C. at the spray dryer's outlet. Microparticlesproduced in this process were recovered using a bag filter in the formof platinum-containing thermoplastic resin microparticles with anaverage diameter of 7 μm and a 0.39 wt. % content of platinum.

REFERENCE EXAMPLE 2

Preparation of Microparticles of a Platinum-Containing PolycarbonateResin

A uniform solution was prepared from 25 kg of a polycarbonate resin (theproduct of Mitsubishi Gas Chemical Co., Inc., trademark “lupilonH-3000”, glass transition point 145 to 150° C.), 40 kg of toluene, 425kg of dichloromethane, 5.0 kg of a toluene solution ofplatinum-1,3-divinyltetramethyidisiloxane complex (with a 2.0 wt. %platinum metal and a 6.0 wt. % 1,3-divinyltetrainethyldichlorosilane),and 0.25 kg of syn-dimethyldiphenyidivinyldisiloxane. The obtaineduniform solution was continuously sprayed via a dual-flow nozzle into aspray-drier through which heated nitrogen gas was directed. Thetemperature of the nitrogen gas was 100° C. at the spray dryer's inletand 70° C. at the spray dryer's outlet. Microparticles produced in thisprocess were recovered using a bag filter in the form ofplatinum-containing polycarbonate resin microparticles with an averagediameter of 1.8 μm and a 0.40 wt. % content of platinum.

PRACTICAL EXAMPLE 1

A room-temperature-curable organopolysiloxane composition was preparedby uniformly mixing the following components under conditions isolatedfrom humid air: 58 parts of a dimethylpolysiloxane having both molecularterminals capped with trimethoxysiloxy groups (viscosity of 16000mPa·s), 6 parts of a dry-process silica powder having the BET-methodspecific surface area of 130 square meters per gram (m2/g)surface-coated with hexamethyidisilazane, 22 parts of quartz powder witha 5 μm average particle diameter, 6 parts of cerium oxide powder with a5 μm average particle diameter, 3 parts of titanium oxide powder with0.2 μm average particle diameter, 1 part of acetylene black (purchasedfrom DENKI KAGAKU KOGYO K.K. as trademark DENKA BLACK) with 35 nanometer(nm) average particle diameter, 2 parts of methyltrinethoxysilane, 2parts of a curing acceleration catalyst in the form of diisopropoxybis(ethylacetate) titanium, and 0.8 parts of the platinum-containingthermoplastic silicone resin prepared in Reference Example 1 (with 32ppm of platinum metal in the compound). The obtained composition wassealed in an aluminum tube. The composition was then loaded into asheet-forming mold and cured for 7 days at 60% relative humidity and at25° C. As a result, a 0.8 mm-thick silicone-rubber sheet was produced.This sheet was cut to form 127 mm-long, 12.7 mm-wide, and 0.8 mm-thickspecimens. The specimens were tested with regard to the initialflame-retarding properties and the same properties after curing. Theresults are shown in Table 1.

PRACTICAL EXAMPLE 2

A room-temperature-curable organopolysiloxane composition was preparedby uniformly mixing the following components under conditions isolatedfrom humid air: 58 parts of a dimethylpolysiloxane having both molecularterminals capped with trimethoxysiloxy groups (viscosity of 16000mPa·s), 6 parts of a dry-process silica powder having the BET-methodspecific surface area of 130 m²/g surface-coated withhexamethyidisilazane, 22 parts of quartz powder with 5 μm averageparticle diameter, 6 parts of cerium oxide powder with 5 μm averageparticle diameter, 3 parts of titanium oxide powder with 0.2 μm averageparticle diameter, 1 part of acetylene black (purchased from DENKIKAGAKU KOGYO K.K. as trademark DENKA BLACK) with a 35 nm averageparticle diameter, 2 parts of methyltrimethoxysilane, 2 parts of acuring acceleration catalyst in the form of diisopropoxybis(ethylacetate) titanium, and 0.8 parts of the platinum-containingthermoplastic silicone resin prepared in Reference Example 2 (with 32ppm of platinum metal in the composition). The obtained composition wassealed in an aluminum tube. The composition was then loaded into asheet-forming mold and cured for 7 days at 60% relative humidity and at25° C. As a result, a 0.8 mm-thick silicone-rubber sheet was produced.This sheet was cut to form 127 mm-long, 12.7 mm-wide, and 0.8 mm-thickspecimens. The specimens were tested with regard to the initialflame-retarding properties and the same properties after curing. Theresults are shown in Table 1.

COMPARATIVE EXAMPLE 1

A room-temperature-curable organopolysiloxane was prepared in the samemanner as in Practical Example 1, with the exception that 0.16 parts ofa toluene solution of a platinum-1,3-divinyltetramethyldisiloxanecomplex (which was an initial raw material for the preparation of aplatinum-containing silicone resin microparticles and which contained2.0 wt. % of platinum metal and 6.0 wt. % of1,3-divinyltetramethyldisiloxane) (the content of platinum metal in theentire composition was 32 ppm) were used instead of theplatinum-containing silicone resin inicroparticles obtained in ReferenceExample 1. The specimens were tested with regard to the initialflame-retarding properties and the same properties after curing. Theresults are shown in Table 1.

COMPARATIVE EXAMPLE 2

A composition was prepared in the same manner as in Practical Example 1,with the exception that the platinum-containing silicone resinmicroparticles were not added. A room-temperature-curableorganopolysiloxane composition was prepared by the same method as inPractical Example 1. Specimens were produced from the obtainedcomposition in the same manner as in Practical Example 1. The specimenswere tested with regard to the initial flame-retarding properties andthe same properties after curing. The results are shown in Table 1.

TABLE 1 Pr. Pr. Comp. Comp. Ex. 1 Ex. 2 Ex. 1 Ex. 2 Composition (parts)Dimethylpolysiloxane 58 58 58 58 Silica powder 6 6 6 6 Quartz powder 2222 22 22 Cerium oxide powder 6 6 6 6 Titanium oxide powder 3 3 3 3Acetylene black 1 1 1 1 Methyltrimethoxysilane 2 2 2 2 Curingacceleration catalyst 2 2 2 2 Platinum-containing silicone resin 0.8microparticles Platinum-containing 0.8 polycarbonate resinmicroparticles Platinum compound 0.16 Content of platinum metal in the32 32 32 0 composition (ppm) Flame-retarding properties Initialflame-retarding properties: Total ignition time 33 15 37 168 (sec.)Maximum ignition time 8 2 8 35 (sec.) Results of evaluation 94V-0 94V-094V-0 Not by UL94 criteria accept- able Flame-retarding properties aftercuring (70° C./7 days) Total ignition time 43 13 54 161 (sec.) Maximumignition time 10 4 21 36 (sec.) Results of evaluation 94V-0 94V-0 94V-1Not by UL94 criteria accept- able Flame-retarding properties aftercuring (150° C./21 days) Total ignition time 55 30 Entirely — (sec.)burned Maximum ignition time 12 7 Entirely — (sec.) burned Results ofevaluation 94V-1 94V-0 Entirely — by UL94 criteria burned 94V-0 meansthat burning stops within 10 seconds after two applications of tenseconds each of a flame to a test bar. No flaming drips are allowed.94V-1 means that burning stops within 60 seconds after two applicationsof ten seconds each of a flame to a test bar. No flaming drips areallowed.

PRACTICAL EXAMPLE 3 To 8, COMPARATIVE EXAMPLE 3 To 5

Components shown in Table 2 (in parts by weight) were uniformly mixedunder conditions isolated from humid air to produce 14 differentroom-temperature-curable organopolysiloxane compositions.

The obtained compositions were sealed in aluminum tubes. Thosecompositions were then loaded into a sheet-forming mold and cured for 7days at 60% relative humidity and at 25° C. As a result, a 0.8 mm-thicksilicone-rubber sheets were produced. These sheets were cut to form 127mm-long, 12.7 mm-wide, and 0.8 mm thick specimens. The specimens weretested with regard to the initial flame-retarding properties and thesame properties after curing. The results are shown in Table 2.

In the attached Table 2, dimethylpolysiloxane had molecular terminalscapped with trimethoxysiloxy groups (viscosity of 16000 mPa·s), platinumcompound was a 1,3-divinyltetramethyldisiloxane solution of aplatinum-1,3-divinyltetramethyldisiloxane complex (OMG Precious MetalsJapan Co., Ltd., trademark Pt-VTSC, 12 wt. % of platinum metal), andplatinum-containing polycarbonate resin microparticles was produced inReference Example 2.

In the Table 2, below inorganic powder were used.

-   -   Quartz powder was purchased from K.K. TATSUMORI as trademark        CRISTALITE VX-S2, Average particle diameter was 5 μm.    -   Titanium oxide powder was purchased from ISHIHARA SANGYO K.K. as        trademark TAIPAQUE R-630, Average particle diameter was 0.2 μm.    -   Aluminum hydroxide powder was purchased from SHOWA DENKO K.K. as        trademark HIGILITE H 42 M. Particle size was 1.1 μm.    -   Zinc carbonate powder was purchased from CHYUO DENKI KOGYO K.K..        Average particle diameter was 9 μm.    -   Aluminum oxide powder was purchased from SHOWA DENKO K.K. as        trademark ALUMINA AS-40. Particle size was 12 μm.    -   Magnesium hydroxide powder was purchased from WAKO PURE CHEMICAL        INDUSTRIES, Ltd..

TABLE 2 Practical Examples Comparative Examples 3 4 5 6 7 8 3 4 5Dimethylpolysiloxane 26.4 23.4 25.4 32.4 9.4 39.8 26.4 23.4 93.6 QuartzPowder 72 72 Titanium oxide powder 75 75 Aluminum hydroxide powder 73Zinc carbonate powder 66 Aluminum oxide powder 90 Magnesium hydroxidepowder 60 Methyltrimethoxysilane 0.8 0.8 0.8 0.8 0.3 1.2 0.8 0.8 3.2Curing accelration catalyst 0.8 0.8 0.8 0.8 0.3 1.2 0.8 0.8 3.2Platinum-containing polycarbonate 0.8 0.8 0.8 0.8 0.8 0.8 0.8 resinmicroparticles Platinum compound 0.027 0.027 Flame-retarding propertiesInitial flame-retarding properties Total ignition time (sec) 46 28 0 1815 4 32 33 Entirely Maximum ignition time (sec) 10 6 0 5 5 2 10 8 burnedResults of evaluation by UL94 criteria 94V-0 94V-0 94V-0 94V-0 94V-094V-0 94V-0 94V-0 Flame-retarding properties after curing (70° C./5days) Total ignition time (sec) 38 30 0 4 7 5 55 69 Entirely Maximumignition time (sec) 10 8 0 2 4 2 14 22 burned Results of evaluation byUL94 criteria 94V-0 94V-0 94V-0 94V-0 94V-0 94V-0 94V-1 94V-1 94V-0means that burning stops within 10 seconds after two applications of tenseconds each of a flame to a test bar. No flaming drips are allowed.94V-1 means that burning stops within 60 seconds after two applicationsof ten seconds each of a flame to a test bar. No flaming drips areallowed.

Practical examples 1 to 8 and Comparative Examples 1 to 5 show that theroom-temperature-curable organopolysiloxane composition of the inventioncomprises aforementioned components (A) through (D), and especially,since it includes component (C) in the form of specificplatinum-containing thermoplastic resin microscopic particlesfunctioning as an agent for imparting to the composition flame-retardingproperties, the composition ensures excellent flame-retarding propertieswhich are not lost in cured silicone articles even after long exposureto high temperatures.

REFERENCE EXAMPLE 3

Preparation of a Platinum Compound Composition

A platinum compound composition (A) was prepared by adding 10 g of1,3-divinyl-1,3-diphenyidimethyldisiloxane to 10 g of a1,3-divinyltetramethyldisiloxane solution of aplatinum-1,3-divinyltetramethyldisiloxane complex (OMG Precious MetalsJapan Co., Ltd., trademark Pt-VTSC, 12 wt. % of platinum metal). Thecomponents were uniformly mixed.

REFERENCE EXAMPLE 4

Preparation of a Platinum Compound Composition

100 g of 1,3-divinyl-1,3-diphenyidimethyldisiloxane were added to 100 gof a 1,3-divinyltetramethyidisiloxane solution ofplatinum-1,3-divinyltetramethyidisiloxane complex (OMG Precious MetalsJapan Co., Ltd., trademark Pt-VTSC, 12 wt. % of platinum metal). Afterthe components were mixed, the 1,3-divinyltetramethyidisiloxane wasremoved by distillation in vacuum under pressure of 0.03 Torr and at atemperature of 50° C. As a result, the platinum compound composition (B)was produced.

PRACTICAL EXAMPLE 9

A room-temperature-curable organopolysiloxane composition was preparedby uniformly mixing the following components under conditions isolatedfrom humid air: 58 parts of a dimethylpolysiloxane having molecularterminals capped with trimethoxysiloxy groups (viscosity of 16000mPa·s), 6 parts of a dry-process silica powder (the BET-method specificsurface area of 130 m²/g) surface-coated with hexamethyldisilazane, 22parts of quartz powder with 5 μm average particle diameter, 6.parts ofcerium oxide powder with 5 μm average particle diameter, 3 parts oftitanium oxide powder with a 0.2 μm average particle diameter, 1 part ofacetylene black (purchased from DENKI KAGAKU KOGYO K.K. as trademarkDENKA BLACK) with 35 nm average particle diameter, 2 parts ofmethyltrimethoxysilane, 2 parts of a curing acceleration catalyst in theform of diisopropoxybis (ethylacetate) titanium, 0.027 parts of1,3-divinyltetramethyldisiloxane solution of platinum-1,3-divinyltetramethyldisiloxane complex (with 32 ppm of platinum metal), and 0.027 partsof 1,3-divinyl-1,3-diphenyldimethyldisiloxane.

The obtained composition was sealed in an aluminum tube. The compositionwas then loaded into a sheet-forming mold and cured for 7 days at 60%relative humidity and at 25° C. As a result, a 0.8 mm-thicksilicone-rubber sheet was produced. This sheet was cut to form 127mm-long, 12.7 mm-wide, and 0.8 mm thick specimens. The specimens weretested with regard to the initial flame-retarding properties and thesame properties after curing. The results are shown in Table 3.

PRACTICAL EXAMPLE 10

A composition was prepared in the same manner as in Practical Example 9,with the exception that, 0.054 parts of the platinum compoundcomposition (A) produced in Reference Example 3 were used instead of the1,3-divinyl-1,3-diphenyldimethyldisiloxane and the1,3-divinyltetramethyidisiloxane solution of theplatinum-1,3-divinyltetramethyidisiloxane complex of Practical Example9. Specimens were produced from the obtained composition in the samemanner as in Practical Example 9. The specimens were tested with regardto the initial flame-retarding properties and the same properties aftercuring. The results are shown in Table 3.

PRACTICAL EXAMPLE 11

A composition was prepared in the same manner as in Practical Example 9,with the exception that, 0.032 parts of the platinum compoundcomposition (B) produced in Reference Example 4 were used instead of the1,3-divinyl-1,3-diphenyidimethyldisiloxane and the1,3-divinyltetramethyldisiloxane solution of theplatinum-1,3-divinyltetramethyldisiloxane complex of Practical Example9. Specimens were produced from the obtained composition in the samemanner as in Practical Example 9. The specimens were tested with regardto the initial flame-retarding properties and the same properties aftercuring. The results are shown in Table 3.

COMPARATIVE EXAMPLE 6

A room-temperature-curable organopolysiloxane was prepared in the samemanner as in Practical Example 9, with the exception the1,3-divinyl-1,3-diphenyldimethyldisiloxane was not added. Specimens wereproduced from the obtained composition in the same manner as inPractical Example 9. The specimens were tested with regard to theinitial flame-retarding properties and the same properties after curing.The results are shown in Table 3.

TABLE 3 Pr. Comp. Ex. 9 Pr. Ex. 10 Pr. Ex. 11 Ex. 6 Composition (parts)Dimethylpolysiloxane 58 58 58 58 Silica powder 6 6 6 6 Quartz powder 2222 22 22 Cerium oxide powder 6 6 6 6 Titanium oxide powder 3 3 3 3Acetylene black 1 1 1 1 Methyltrimethoxysilane 2 2 2 2 Curingacceleration catalyst 2 2 2 2 Platinum-1,3- 0.027 0.027divinyltetramethyldisiloxane complex 1,3-divinyl-1,3- 0.027diphenyldimethyldisiloxane Platinum compound (A) 0.054 Platinum compound(B) 0.032 Content of platinum metal in 32 32 32 32 the compound (ppm)Flame-retarding properties Initial flame-retarding properties: Totalignition time (sec.) 22 16 12 37 Maximum ignition time 5 4 4 8 (sec.)Results of evaluation 94V-0 94V-0 94V-0 94V-0 by UL94 criteriaFlame-retarding properties after curing (70° C./7 days) Total Ignitiontime (sec) 16 12 10 54 Maximum ignition time 3 3 3 21 (sec.) Results ofevaluation 94V-0 94V-0 94V-0 94V-1 by UL94 criteria 94V-0 means thatburning stops within 10 seconds after two applications of ten secondseach of a flame to a test bar. No flaming drips are allowed. 94V-1 meansthat burning stops within 60 seconds after two applications of tenseconds each of a flame to a test bar. No flaming drips are allowed.

Practical Examples 9, 10, and 11 and Comparative Example 6 show that theroom-temperature-curable organopolysiloxane composition of the inventionconsists of aforementioned components (A) through (D), and especially,since it includes component (C1) in the form of a platinum compound andcomponent (C2) in the form of an organopolysiloxane with an aryl groupand an alkenyl group, the composition ensures excellent flame-retardingproperties which are not lost in cured silicone articles even after longexposure to high temperatures. Furthermore, the invention provides amethod for efficient manufacturing of the aforementionedroom-temperature-curable organopolysiloxane composition.

1. A condensation-curable organopolysiloxane composition consistingessentially of: (A) 100 parts by weight of an organopolysiloxane havinga viscosity from 100 to 500,000 mPa·s at 25° C. and having in onemolecule 1.5 or more end groups represented by the following generalformula: (X)_(a)R¹ _(3−a)Si—, wherein each X is independently selectedfrom the group consisting of a hydroxyl group and a hydrolyzable group,each R¹ is independently selected from the group consisting of amonovalent hydrocarbon group and a halogen-substituted monovalenthydrocarbon group, and a is 1, 2, or 3; (B) 0.01 to 40 parts by weightof a cross-linking agent selected from a group consisting of a silane ora siloxane oligomer, wherein the cross-linking agent has three or moresilicon-bonded hydrolyzable groups per molecule; (C1) a flame retardantcomprising a platinum compound present in an amount such that metallicplatinum is present in an amount of 1 to 2,000 ppm based on the weightof the composition; (C2) an organosiloxane oligomer, where theorganosiloxane oligomer contains aryl and alkenyl groups, theorganosiloxane oligomer has 8 or less silicon atoms per molecule, andthe organosiloxane oligomer contains in each molecule at least onedivalent organosiloxane group represented by the formula—(R²)(R³)SiO—(R²)(R³)Si— wherein R² is an aryl group, and R³ is analkenyl group; wherein the organosiloxane oligomer is present in aquantity such that the composition contains at least 2 moles ofcomponent (C2) per 1 mole of platinum atoms in component (C1); and (D) 5to 300 parts by weight of an inorganic powder.
 2. The composition ofclaim 1, where component (C1) is a platinum complex having as a ligandan organosiloxane which contains alkyl and alkenyl groups having in onemolecule at least one divalent organosiloxane group shown by formula:—(R³)(R⁴)SiO—(R³)(R⁴)Si—, wherein R³ is an alkenyl group, and R⁴ is analkyl group with 6 or less carbon atoms, component (C1) contains in onemolecule an alkyl group and an alkenyl group, and component (C1) has 8or less silicon atoms; or a mixture of the organosiloxane with theplatinum complex.
 3. The composition of claim 1, wherein component (C2)is 1,3-divinyl-1,3-diphenyldimethyldisiloxane.
 4. The composition ofclaim 1 wherein each X in component (A) is independently an alkoxygroup, and each hydrolyzable group in component (B) is independently analkoxy group.
 5. The composition of claim 1, wherein component (D) isselected from the group consisting of a reinforcing silica powder,quartz powder, cerium oxide powder, titanium oxide powder, carbon black,aluminum hydroxide powder, calcium carbonate powder, aluminum oxidepowder, magnesium hydroxide powder, magnesium carbonate powder, zinccarbonate powder, or a mixture thereof.
 6. The composition of claim 5,where the reinforcing silica powder is a dry-process silica.
 7. Thecomposition of claim 6, where the surface of the dry-process silica istreated with a hydrophobic agent selected from the group consisting of atrimethylchlorosilane, dimethylchlorosilane, hexamethyldisilazane, andoctamethylcyclotetrasiloxane.
 8. The composition of claim 1 whereincomponent (D) is a mixture of a reinforcing silica powder, quartzpowder, cerium oxide powder, and carbon black.
 9. The composition ofclaim 1 wherein component (D) is a mixture of a reinforcing silicapowder, quartz powder, cerium oxide powder, titanium oxide powder, andcarbon black.
 10. A composition as set forth in claim 1 having a maximumignition time of 10 seconds or less as determined by UL94.
 11. Acomposition as set forth in claim 1 that is cured and has a maximumignition time of 12 seconds or less as determined by UL94.
 12. A methodof preparing a condensation-curable organopolysiloxane compositioncomprising the steps of: (1) adding (C1) a flame retardant comprising aplatinum compound, in an amount such that metallic platinum is presentin an amount of 1 to 2,000 ppm based on the weight of thecondensation-curable organopolysiloxane composition, to a compositioncomprising: (A) 100 parts by weight of an organopolysiloxane having aviscosity from 100 to 500,000 mPa·s at 25° C. and having in one molecule1.5 or more end groups represented by the following general formula:(X)_(a)R¹ _(3−a)Si—, where each X is independently selected from thegroup consisting of a hydroxyl group and a hydrolyzable group, each R¹is independently selected from the group consisting of a monovalenthydrocarbon group and a halogen-substituted monovalent hydrocarbongroup, and a is 1, 2, or 3; (B) 0.01 to 40 parts by weight of across-linking agent selected from a group consisting of a silane or asiloxane oligomer, wherein the cross-linking agent has three or moresilicon-bonded hydrolyzable groups per molecule; (C2) an organosiloxaneoligomer, where the organosiloxane oligomer contains aryl and alkenylgroups, the organosiloxane oligomer has 8 or less silicon atoms permolecule, and the organosiloxane oligomer contains in each molecule atleast one divalent organosiloxane group as represented by the formula—(R²)(R³)SiO—(R²)(R³)Si— wherein R² is an aryl group, and R³ is analkenyl group; where the organosiloxane oligomer is present in aquantity such that the composition contains at least 2 moles ofcomponent (C2) per 1 mole of platinum atoms in component (C1); and (D) 5to 300 parts by weight of an inorganic powder; and (2) curing thecondensation-curable organopolysiloxane composition via a condensationreaction, wherein the condensation-curable organopolysiloxanecomposition consists essentially of the (A) organopolysiloxane, the (B)cross-linking agent, the (C1) flame retardant, the (C2) organosiloxaneoligomer, and the (D) inorganic powder.
 13. A method as set forth inclaim 12 wherein the composition has a maximum ignition time of 10seconds or less as determined by UL94.
 14. A method as set forth inclaim 12 wherein the composition that is cured has a maximum ignitiontime of 12 seconds or less as determined by UL94.
 15. A product preparedby the method of claim
 12. 16. A method of preparing acondensation-curable organopolysiloxane composition comprising the stepsof: (1) pre-mixing (C1) a flame retardant comprising a platinumcompound, in an amount such that metallic platinum is present in anamount of 1 to 2,000 ppm based on the weight of the condensation-curableorganopolysiloxane composition, with (C2) an organosiloxane oligomer,where the organosiloxane oligomer contains aryl and alkenyl groups, theorganosiloxane oligomer has 8 or less silicon atoms per molecule, andthe organosiloxane oligomer contains in each molecule at least onedivalent organosiloxane group as represented by the formula—(R²)(R³)SiO—(R²)(R³)Si— wherein R² is an aryl group, and R³ is analkenyl group; where the organosiloxane oligomer is present in aquantity such that the composition contains at least 2 moles ofcomponent (C2) per 1 mole of platinum atoms in component (C1) to form amixture; (2) combining the mixture with: (A) 100 parts by weight of anorganopolysiloxane having a viscosity from 100 to 500,000 mPa·s at 25°C. and having in one molecule 1.5 or more end groups represented by thefollowing general formula: (X)_(a)R¹ _(3−a)Si—, where each X isindependently selected from the group consisting of a hydroxyl group anda hydrolyzable group, each R¹ is independently selected from the groupconsisting of a monovalent hydrocarbon group and a halogen-substitutedmonovalent hydrocarbon group, and a is 1, 2, or 3; (B) 0.01 to 40 partsby weight of a cross-linking agent selected from a group consisting of asilane or a siloxane oligomer, wherein the cross-linking agent has threeor more silicon-bonded hydrolyzable groups per molecule; and (D) 5 to300 parts by weight of an inorganic powder to form thecondensation-curable organopolysiloxane composition; and (3) curing thecondensation-curable organopolysiloxane composition via a condensationreaction, wherein the condensation-curable organopolysiloxanecomposition consists essentially of the (A) organopolysiloxane, the (B)cross-linking agent, the (C1) flame retardant, the (C2) organosiloxaneoligomer, and the (D) inorganic powder.
 17. A method as set forth inclaim 16 wherein the composition has a maximum ignition time of 10seconds or less as determined by UL94.
 18. A method as set forth inclaim 16 wherein the composition that is cured has a maximum ignitiontime of 12 seconds or less as determined by UL94.